1. Field of the Invention
The present invention relates to a process for producing a cyclized polymer of isoprene having a dispersion degree not greater than 2 as defined as the ratio of Mw/Mn, where Mw and Mn are the weight-average and the number-average molecular weights, respectively.
More particularly, the present invention relates to a process for producing a cyclized polymer of isoprene having a dispersion degree not greater than 2, comprising polymerizing isoprene monomers in the presence of an organometallic compound expressed by a general formula RM, where R is alkyl, aryl or aralkyl group and M is lithium, sodium or potassium atom, and bringing the obtained polymer of a low dispersion degree into contact with a catalyst which comprises a boron trifluoride-ether complex and a carboxylic acid expressed by a general formula Cl.sub.3-n H.sub.n CCOOH, where n is an integer ranging from 0 to 3.
Cyclized compounds of natural or synthetic rubbers have been most widely used as a negative resist substance, which becomes insoluble in solvents on irradiation with light, due to the crosslinkage formed between high polymer chains.
Among various properties of the resist substances, two particularly important properties are sensitivity and resolution. With improvements recently made in the integration degree of integrated circuits, increasing demands have been made for a higher resolution degree of the resist substances. Today, materials are in particular demand which permit a microprocessing precision of 1 .mu.m or less.
2. Description of Prior Arts
The conventional rubber resist materials mentioned above have presented problems with respect to their resolution ability, and their dimensional accuracy limit which is practically laid at about 3 .mu.m. Thus, the conventional materials cannot meet the requirements of the production processes of integrated circuits of higher integration degree, which require a precision accuracy of less than 3 .mu.m.
The conventional rubber resists, whether of natural or synthetic rubbers, have a wide distribution of molecular weights, and their dispersion degree as defined as a ratio of Mw/Mn is usually greater than 2 or 3, where Mw and Mn are the weight-average and number-average molecular weights, respectively.
Conventional methods for cyclization of diene polymers include:
(1) a method using sulfuric or sulfonic acid; PA1 (2) a method using the Friedel-Crafts' catalyst, such as SnCl.sub.4, TiCl.sub.4 and FeCl.sub.3 ; PA1 (3) a method using a hydrogen halogenide, such as hydrogen chloride; PA1 (4) a method using a phosphorus compound, such as phosphorus pentachloride and phosphorus oxychloride; and PA1 (5) a method using a cationic polymerization initiator, such as a catalyst composed of trichloroacetic acid and either of diethyl aluminum chloride and ethyl aluminum dichloride.
According to these conventional methods, however, reactions such as gel formation occur among high molecular chains, and it is difficult to selectively enforce the cyclization reaction in molecules.